1 Pertemuan 19 Disk Matakuliah: T0316/sistem Operasi Tahun: 2005 Versi/Revisi: 5 OFFCLASS03

2 Learning Outcomes Pada akhir pertemuan ini, diharapkan mahasiswa akan mampu : menjelaskan perangkat-perangkat disk dan cara kerjanya (C2)

3 Outline Materi Disk Hardware RAID CDROM DVD Interleaving Disk Arm Scheduling

4 Disks Disk parameters for the original IBM PC floppy disk and a Western Digital WD hard disk Disk Hardware (1)

5 Disk Hardware (2) Physical geometry of a disk with two zones A possible virtual geometry for this disk

6 Disk Hardware (3) Raid levels 0 through 2 Backup and parity drives are shaded Split on write Primary & backup

7 Disk Hardware (4) Raid levels 3 through 5 Backup and parity drives are shaded

8 Disk Hardware (5) Recording structure of a CD or CD-ROM

9 Disk Hardware (6) Logical data layout on a CD-ROM

10 Disk Hardware (7) Cross section of a CD-R disk and laser –not to scale Silver CD-ROM has similar structure –without dye layer –with pitted aluminum layer instead of gold

11 Disk Hardware (8) A double sided, dual layer DVD disk

12 Disk Formatting (1) A disk sector

13 Disk Formatting (2) An illustration of cylinder skew

14 Disk Formatting (3) No interleaving Single interleaving Double interleaving

15 Disk Arm Scheduling Algorithms (1) Time required to read or write a disk block determined by 3 factors 1.Seek time 2.Rotational delay 3.Actual transfer time Seek time dominates Error checking is done by controllers

16 FCFS Eg. –Disk with 40 cylinders –Request comes from cylinder 11 –New requests come from cylinder 1, 36, 16, 34, 9, and 12 –Total of arm motions: 10, 35, 20, 18, 25 and 3. Disk Arm Scheduling Algorithms (1)

17 Disk Arm Scheduling Algorithms (2) Shortest Seek First (SSF) disk scheduling algorithm

18 Disk Arm Scheduling Algorithms (3) The elevator algorithm for scheduling disk requests